Chapter 12 Alkenes, Alkynes, and Aromatic Compounds

1. Chapter 12 Alkenes, Alkynes, and Aromatic Compounds 12.5 Aromatic Compounds

2. Benzene Structure Benzene • has 6 electrons shared equally among the 6 C atoms • is also represented as a hexagon with a circle drawn inside

3. Aromatic Compounds in Nature and Health

4. Naming Aromatic Compounds Aromatic compounds are named • with benzene as the parent chain • with one side group named in front of benzene Methylbenzene Chlorobenzene

5. Some Common Names Some substituted benzene rings • have common names that have been used for many years • with a single substituent use a common name or are named as a benzene derivative. Toluene Aniline Phenol (methylbenzene) (benzenamine) (hydroxybenzene)

6. Aromatic Compounds with Two Groups When two groups are attached to a benzene ring, • number the ring to give the lowest numbers to the side groups (IUPAC) or • use prefixes to show the arrangement of the substituents (common) on the ring ortho (o) for 1,2- meta (m) for 1,3- para (p) for 1,4-

7. Examples of Aromatic Compounds with Two Groups 3-Chlorotoluene 1,4-Dichlorobenzene 2-Chlorophenol (m-chlorotoluene) (p-dichlorobenzene) (o-chlorophenol) Substituent's on 1st and 3rd carbons 1st and 4th carbons 1st and 2nd carbons

8. Xylene For isomers of dimethylbenzene, • the common name xylene may be used

9. Learning Check Select the correct name(s) for each of the following compounds: 1) chlorocyclohexane 2) chlorobenzene 3) 1-chlorobenzene 1) 1,2-dimethylbenzene 2) 1,3-dimethylbenzene 3) m-xylene

10. Solution Select the correct name(s) for each of the following compounds: 2) chlorobenzene 2) 1,3-dimethylbenzene 3) m-xylene

11. Learning Check Draw the condensed structural formulas for each of the following: A. 1,3-Dichlorobenzene B. o-Chlorotoluene

12. Solution Draw the condensed structural formulas for each of the following: A. 1,3-Dichlorobenzene B. o-Chlorotoluene

13. Learning Check Identify the organic family for each of the following: A. CH3─CH2─CH═CH2 B. C. CH3─C≡CH D.

14. Solution Identify the organic family for each of the following: A. CH3─CH2─CH═CH2 alkene B. cycloalkane (alkane) C. CH3─C≡CH alkyne D. aromatic

15. Properties of Aromatic Compounds Aromatic compounds • have a stable aromatic bonding system • are resistant to many reactions • undergo substitution reactions, which retain the stability of the aromatic bonding system

16. Substitution Reactions In a substitution reaction, a hydrogen atom on a benzene ring is replaced by an atom or group of atoms. Type of substitution H on benzene replaced by • Halogenation Chlorine or bromine atom • Nitration Nitro group (—NO2) • Sulfonation —SO3H group

17. Halogenation In the halogenationof benzene • an H atom of benzene is replaced by a chlorine or bromine atom • a catalyst such as FeCl3 is needed in chlorination • a catalyst such as FeBr3 is needed in bromination

18. Nitration In the nitration of benzene, • an H atom of benzene is replaced by a nitro (–NO2) group from HNO3 • an acid catalyst such as H2SO4 is needed

19. Sulfonation In the sulfonationof benzene, • an H atom on benzene is replaced by a —SO3H group from SO3 • an acid catalyst such as H2SO4 is needed

20. Learning Check Write the equation for the bromination of benzene, including the catalyst.

21. Solution Write the equation for the bromination of benzene, including the catalyst.